In the past, one method of providing an opening for the air crew through the canopy area was by jettisoning the entire canopy transparency and metal frame structure from the aircraft. A second method has been to blast and fragment the transparency with a directed charge thereby permitting removal of the transparency from the metal frame and the aircraft structure. In this second method a detonating cord is placed against the transparency in order to accomplish fragmentation. It has been found that where the detonating cord is affixed to the inside of the canopy, the cord is exposed to environmental changes as well as abrasion from crew movement within the cockpit. Accordingly, it has been necessary to shield the detonating cord to protect it and maintain its operability.
With the advent of faster aircraft and the desire to provide greater cockpit visibility, canopy structural support members have been reduced and greater loads have been placed directly upon the canopy transparency. When a full bubble canopy is utilized, it has been necessary to use thicker canopy transparency material or one which is stronger, such as a polycarbonate.
When the strength of the canopy transparency increases, it is necessary to increase the explosive charge adjacent the canopy surface to fragment the canopy transparency for removal. Even though the explosive charge is shielded from the crew, the explosion, hot gasses and fragmentation of the canopy has had undesirable effects on the crew environment. In addition to noise and blast effects, crews have been subjected to vision impairment from the explosive materials, and lead burn from high velocity metal particles from the detonating cord. It has been calculated that the explosion of a detonating cord of sufficient size mounted in accordance with the present state of the art to fragment a 3/4 inch thick polycarbonate canopy could prove debilitating to the crew within the aircraft.